With the development of electronic devices having higher performance, a smaller size, and a smaller thickness, there has recently been a strong demand for an increase in the density of and reduction in the thickness of electronic circuits and integrated circuits of the electronic devices.
Such a conductive pattern that can be used for an electronic circuit or the like is, for example, a known conductive pattern produced by coating a surface of a support with a conductive ink or a plating nucleating agent containing a conductive substance such as silver and firing the coated substance to form a conductive substance layer; and subsequently by plating the surface of the conductive substance layer to form a plating layer on the surface of the conductive substance layer (for example, refer to Patent Literature 1).
However, in the conductive pattern, the adhesion between the support and the conductive substance layer is insufficient. Accordingly, in some cases, with passage of time, the conductive substance becomes separated from the surface of the support, which causes disconnection in the conductive pattern formed of the conductive substance or degradation of conductivity (increase in resistance).
As a method for enhancing the adhesion between the support and the conductive substance, for example, there is a known method of producing a conductive pattern in which a pattern is formed in a predetermined manner with a conductive ink on an ink-receiving substrate in which a latex layer is formed on the surface of a support (refer to Patent Literature 2).
However, the conductive pattern obtained by this method is still insufficient in terms of adhesion between the support and the ink-receiving layer in some cases. Accordingly, with passage of time, the ink-receiving layer and the conductive substance become separated from the surface of the support, which causes disconnection in the conductive pattern formed of the conductive substance or degradation of conductivity in some cases. In other cases, upon use of the conductive pattern in a high temperature or high humidity environment, the adhesion is considerably degraded, which sometimes results in separation of the conductive substance.
The separation of the ink-receiving layer from the surface of the support occurs upon, for example, heating at about 100° C. to about 200° C. during the plating step and sufficiently high resistance to humidity and heat is not provided. For this reason, in some cases, the conductive pattern cannot be subjected to plating intended to enhance the strength, for example.
In order to achieve a higher density of electronic circuits and the like, a technique of producing a multilayer conductive pattern is under study. Specifically, in this technique, on the surface of a conductive layer or a plating layer of an existing conductive pattern, a second conductive layer is further formed.
However, during formation of the second conductive layer, a film-shaped insulating layer is formed between the conductive layers or a primer layer is formed on the surface of the film-shaped insulating layer for the purpose of enhancing adhesion to the second conductive layer in some cases. This tends to result in an excessively large thickness of the electronic circuit.